Azeotrope-like compositions of 1,1,1,3,3-pentafluorobutane and hydrogen fluoride

ABSTRACT

The invention relates to azeotropic and azeotrope-like mixtures of 1,1,1,3,3-pentafluorobutane (HFC-365) and hydrogen fluoride and a process for separating the azeotrope-like mixtures. The compositions of the invention are useful as an intermediate in the production of HFC-365. The latter is useful as a nontoxic, zero ozone depleting fluorocarbon useful as a solvent, blowing agent, refrigerant, cleaning agent and aerosol to propellant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of parent U.S. application Ser. No.10/160,673 which was filed with the United States Patent and TrademarkOffice on Jun. 3, 2002 now U.S. Pat. No. 6,673,264 and which, in turn,claims priority to provisional Application Ser. No. 60/295,049, whichwas filed with the United States Patent and Trademark Office on Jun. 1,2001. The aforementioned parent and provisional applications areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to azeotropic and azeotrope-likecompositions of 1,1,1,3,3-pentafluorobutane (HFC-365) and hydrogenfluoride.

BACKGROUND

Fluorocarbon based fluids have found widespread use in industry in anumber of applications, including as refrigerants, aerosol propellants,blowing agents, heat transfer media, and gaseous dielectrics. Because ofthe suspected environmental problems associated with the use of some ofthese fluids, it is desirable to use fluids having low or even zeroozone depletion potential, such as hydrofluorocarbons (“HFC's”). Thus,the use of fluids that do not contain chlorofluorocarbons (“CFCs”) orhydrochlorofluorocarbons (“HCFCs”) is desirable. Additionally, the useof single component fluids or azeotropic mixtures, which do notfractionate on boiling and evaporation, is desirable. However, theidentification of new, environmentally-safe, non-fractionating mixturesis complicated due to the fact that azeotrope formation is not readilypredictable.

The industry is continually seeking new fluorocarbon based mixtures thatoffer alternatives to, and are considered environmentally safersubstitutes for, CFC's and HCFCs. Of particular interest arecombinations or mixtures containing 1,1,3,3-pentafluorobutane (HFC-365)and an acid, both having low ozone depletion potentials. (HFC-365 iswell known in the art and is described in U.S. Pat. Nos. 5,917,098;5,395,997; 4,950,364; and 5,208,398, which are incorporated herein byreference.) Such mixtures are the subject of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present inventors have developed several compositions that can helpto satisfy the continuing need for substitutes for CFCs and HCFCs. Inone embodiment, the present invention provides azeotrope-likecompositions comprising 1,1,1,3,3-pentafluorobutane (“HFC-365 mfc”) andhydrogen fluoride (“HF”).

It is known that the composition of an azeotropic mixture varies withpressure variations in that the relative concentrations of thecomponents of the azeotropic mixture will change with pressure. However,the degree to which a particular azeotropic mixture will vary withpressure is unpredictable. Accordingly, it is also unpredictable whethertwo compounds with close boiling points in azeotropic admixture can beseparated by distillation which takes advantage of the pressurevariation effect (for example, pressure swing distillation).

Applicants have discovered that the relative concentrations of thecomponents of the 1,1,1,3,3-pentafluorobutane/hydrogen fluorideazeotrope-like composition change to a significant degree, and more thanone skilled in the art would expect, as the pressure to which theazeotrope-like composition is exposed is changed. Such a significantcomposition differential facilitates separation because, in certainpreferred embodiments, either 1,1,1,3,3-pentafluorobutane or hydrogenfluoride will concentrate in the distillate during distillation at onepressure, and then, upon distillation of the distillate at a differentpressure, will tend to concentrate in the bottoms. This way, thecomponent can be removed from the mixture through the bottoms.

Since these pressures are within the operating parameters ofconventional distillation equipment, the process of the presentinvention can be practiced using existing equipment with little or nomodification.

Accordingly, in another embodiment, the present invention provides aprocess for separating 1,1,1,3,3-pentafluorobutane from an1,1,1,3,3-pentafluorobutane/hydrogen fluoride azeotropic mixture, whichprocess comprises, consists essentially of, or consists of the steps of:

(A) distilling a mixture comprising an azeotropic mixture of1,1,1,3,3-pentafluorobutane and hydrogen fluoride at a first pressure toproduce a first overhead stream enriched in either1,1,1,3,3-pentafluorobutane or hydrogen fluoride and a first bottomsstream enriched in the other component; and

(B) redistilling the first overhead stream at a second pressure toproduce a second overhead stream enriched in the component enriched inthe first bottoms stream and a second bottoms stream enriched in thecomponent enriched in the first overhead stream.

The invention also provides a method of forming an azeotropic orazeotrope-like composition which consists essentially of blending1,1,1,3,3-pentafluorobutane and hydrogen fluoride.

The term “enriched” is used herein to refer to the condition during thedistillation of a mixture in which the concentration of one component ineither the distillate or a bottoms product is higher relative to itsconcentration in the mixture.

The invention still further provides a process for removing1,1,1,3,3-pentafluorobutane from a mixture containing1,1,1,3,3-pentafluorobutane and at least one impurity, which comprisesadding hydrogen fluoride to the mixture in an amount sufficient to forman azeotropic or azeotrope-like composition of the1,1,1,3,3-pentafluorobutane and the hydrogen fluoride, and thereafterseparating the azeotropic composition from the impurity.

Compositions

The present compositions are azeotrope-like compositions. As usedherein, the term “azeotrope-like” is intended in its broad sense toinclude both compositions that are strictly azeotropic and compositionsthat behave like azeotropic mixtures. From fundamental principles, thethermodynamic state of a fluid is defined by pressure, temperature,liquid composition, and vapor composition. An azeotropic mixture is asystem of two or more components in which the liquid composition andvapor composition are equal at the state pressure and temperature. Inpractice, this means that the components of an azeotropic mixture areconstant boiling and cannot be separated during a phase change.

Azeotrope-like compositions are constant boiling or essentially constantboiling. In other words, for azeotrope-like compositions, thecomposition of the vapor formed during boiling or evaporation isidentical, or substantially identical, to the original liquidcomposition. Thus, with boiling or evaporation, the liquid compositionchanges, if at all, only to a minimal or negligible extent. This is tobe contrasted with non-azeotrope-like compositions in which, duringboiling or evaporation, the liquid composition changes to a substantialdegree. All azeotrope-like compositions of the invention within theindicated ranges as well as certain compositions outside these rangesare azeotrope-like.

The azeotrope-like compositions of the invention may include additionalcomponents that do not form new azeotrope-like systems, or additionalcomponents that are not in the first distillation cut. The firstdistillation cut is the first cut taken after the distillation columndisplays steady state operation under total reflux conditions. One wayto determine whether the addition of a component forms a newazeotrope-like system so as to be outside of this invention is todistill a sample of the composition with the component under conditionsthat would be expected to separate a non-azeotropic mixture into itsseparate components. If the mixture containing the additional componentis non-azeotrope-like, the additional component will fractionate fromthe azeotrope-like components. If the mixture is azeotrope-like, somefinite amount of a first distillation cut will be obtained that containsall of the mixture components that is constant boiling or behaves as asingle substance.

It follows from this that another characteristic of azeotrope-likecompositions is that there is a range of compositions containing thesame components in varying proportions that are azeotrope-like orconstant boiling. All such compositions are intended to be covered bythe terms “azeotrope-like” and “constant boiling”. As an example, it iswell known that at differing pressures, the composition of a givenazeotrope will vary at least slightly as does the boiling point of thecomposition. Thus, an azeotrope of A and B represents a unique type ofrelationship, but with a variable composition depending on temperatureand/or pressure. It follows that, for azeotrope-like compositions, thereis a range of compositions containing the same components in varyingproportions that are azeotrope-like. All such compositions are intendedto be covered by the term azeotrope-like as used herein.

The present invention provides azeotrope and azeotrope-like compositionscomprising 1,1,1,3,3-pentafluorobutane and hydrogen fluoride.Preferably, the novel azeotrope-like compositions of the presentinvention comprise effective amounts of hydrogen fluoride and1,1,1,3,3-pentafluorobutane. The term “effective amounts” as used hereinrefers to the amount of each component which upon combination with theother component or components, results in the formation of the presentazeotrope-like compositions.

The inventive compositions are preferably binary azeotropes whichconsist essentially of hydrogen fluoride with1,1,1,3,3-pentafluorobutane. In the certain embodiments, the inventivecompositions consist essentially of from about 1 to about 95 weightpercent 1,1,1,3,3-pentafluorobutane and from about 5 to about 99 weightpercent hydrogen fluoride, preferably the inventive compositions consistessentially of from about 5 weight percent to about 90 weight percent1,1,1,3,3-pentafluorobutane and about 10 to about 95 weight percenthydrogen fluoride. In certain more preferred embodiments, the presentcompositions consist essentially of about 4 weight percent to about 10weight percent hydrogen fluoride and about 90 to about 96 weight percent1,1,1,3,3-pentafluorobutane.

The compositions of the present invention have a vapor pressure of about15 psia to about 22 psia at about 20.2° C. or a vapor pressure of about29 psia to about 36 psia at about 40.2° C. By way of example, anazeotrope-like composition having about 6.8±3 weight percent hydrogenfluoride and about 73.2±3 weight percent 1,1,1,3,3-pentafluorobutane hasbeen found to have a vapor pressure of about 18.15 psia at about 20.2°C. An azeotrope-like composition having about 6.8±3 weight percenthydrogen fluoride and about 73.2±3 weight percent1,1,1,3,3-pentafluorobutane has been found to have a vapor pressure ofabout 32.19 psia at about 40.2° C.

Uses of the Compositions

The compositions of the present invention may be used in a wide varietyof applications as substitutes for CFCs and HCFCs. For example, thepresent compositions are useful as solvents, blowing agents,refrigerants, cleaning agents and aerosols. In addition, thecompositions of the present invention are particularly suited for use inproducing relatively pure 1,1,1,3,3-pentafluorobutane.

In one embodiment, the present invention provides methods for separating1,1,1,3,3-pentafluorobutane from an azeotropic mixture of1,1,1,3,3-pentafluorobutane and hydrogen fluoride, which processcomprises the steps of:

(A) distilling a mixture comprising an azeotropic mixture of1,1,1,3,3-pentafluorobutane and hydrogen fluoride at a first pressure toproduce a first overhead stream enriched in either the1,1,1,3,3-pentafluorobutane or the hydrogen fluoride and a first bottomsstream enriched in the other component; and

(B) redistilling the first overhead stream at a second pressure toproduce a second overhead stream enriched in the component enriched inthe first bottoms stream and a second bottoms stream enriched in thecomponent enriched in the first overhead stream.

Any mixture comprising an azeotropic mixture of1,1,1,3,3-pentafluorobutane and hydrogen fluoride may be used in thepresent methods. While such mixtures may be provided via anyconventional source, in certain preferred embodiments, the mixtures aresupplied as a products stream resulting from a manufacturing processincluding, for example, the manufacture of fluorocarbons. In suchpreferred embodiments, the by-products, reactants, and reactionintermediates of the fluorocarbon production process may be present inthe mixture along with 1,1,1,3,3-pentafluorobutane and hydrogenfluoride.

The methods of the present invention may be performed using a singledistillation column or a series of distillation columns. In embodimentswherein a single distillation column is used, the methods of the presentinvention are typically performed as batch distillations. The mixturemay be fed, for example, into a batch distillation column operating at afirst pressure. The distillate is then collected and refed into thecolumn at a second pressure. Preferably, the methods of the presentinvention are performed using a series of distillation columns, meaningat least two columns, operating at different pressures in a batch orcontinuous distillation. Examples of distillation columns and methodssuitable for use in the present invention are disclosed in U.S. Pat. No.5,918,481 (issued to AlliedSignal), which is incorporated herein byreference.

Whether the distillation process is continuous or batch, the pressuresat which the distillations are conducted preferably are such thatconventional distillation apparatus can be used. In preferredembodiments, one distillation pressure is higher than anotherdistillation pressure used. The higher distillation pressure generallymay range from about 50 to about 400 psia, preferably about 100 to about250, more preferably about 150 to 220 psia. The lower distillationpressure generally may range from about 5 psia to about 50 psia,preferably from about 5 psia to less than about 35, more preferably fromabout 5 psia to less than about 25, and even more preferably from about5 psia to less than about 20 psia.

The temperatures at which these distillations are performed are directlyrelated to the boiling points and pressures used, and are well withinthe scope of knowledge of one skilled in the art.

In certain other embodiments, the present invention provides a methodfor removing 1,1,1,3,3-pentafluorobutane from a mixture containing1,1,1,3,3-pentafluorobutane and at least one impurity. As used herein,the term “impurity” refers to any compound present in a mixture with1,1,1,3,3-pentafluorobutane from which it is desirable, for a givenapplication, to separate the 1,1,1,3,3-pentafluorobutane. Preferably,the impurity itself does not form an azeotrope-like mixture with1,1,1,3,3-pentafluorobutane, hydrogen fluoride or a mixture of1,1,1,3,3pentafluorobutane and hydrogen fluoride. Typical impuritiesinclude other halocarbons which may be miscible with1,1,1,3,3-pentafluorobutane such as, for example,1,1,1,3,3-hexachlorobutane (HCC-360).

The method for separating 1,1,1,3,3-pentafluorobutane and at least animpurity comprises adding hydrogen fluoride to the mixture in an amountsufficient to form an azeotrope-like composition of the1,1,1,3,3-pentafluorobutane and the hydrogen fluoride, and thenseparating the azeotropic composition from the mixture.

The azeotropic composition of the present method may be separated fromthe mixture comprising the impurity by any of a number of conventionalmethods. Examples of separation methods include, for example,distillation, scrubbing, other art-recognized separating means, andcombinations of two or more thereof.

Any mixture containing 1,1,1,3,3-pentafluorobutane and at least oneimpurity may be used in the present method. While such mixtures may beprovided via any conventional source, in certain preferred embodiments,the mixtures are reaction products resulting from a manufacturingprocess, most notably, the production of 1,1,1,3,3-pentafluorobutane.

Those of skill in the art will recognize that the amount of hydrogenfluoride to be added to the mixture, and to form an azeotrope-likecomposition, will depend on the conditions under which theazeotrope-like composition is formed. In light of the disclosure herein,those of skill in the art will be readily able to determine the amountsof hydrogen fluoride necessary to form azeotrope-like compositions with1,1,1,3,3-pentafluorobutane under a wide range of pressures andtemperatures.

The following non-limiting examples serve to illustrate the invention.

EXAMPLE 1

Binary compositions consisting essentially of1,1,1,3,3-pentafluorobutane (HFC-365 mfc) and hydrogen fluoride areblended to form homogeneous mixtures having different compositions. Thevapor pressures of the mixtures were measured at 20.2° C. and 40.2° C.

Table 1 shows the vapor pressure measurement of1,1,1,3,3-pentafluorobutane and hydrogen fluoride as a function ofcomposition of weight percent hydrogen fluoride at two constanttemperatures of 20.2° C. and 40.2° C. From this data it is observed thatat 20.2° C. the composition exhibits azeotrope-like properties at about6.8 weight percent. Based on further observations made during theexperiment, it is determined that the composition at which the vaporpressure is the maximum is about 4 weight percent hydrogen fluoride orbetween about 4 and 8 weight percent hydrogen fluoride at 20.2° C. Basedon further observations made during the experiment, it is determinedthat the composition at which the vapor pressure is the maximum at 40.2°C. is about 8 weight percent hydrogen fluoride or between about 4 and 10weight percent hydrogen fluoride. From this example it is determinedthat the azeotropic composition is about 4 weight percent hydrogenfluoride at 20.2° C. and about 8 weight percent hydrogen fluoride at40.2° C.

TABLE 1 WEIGHT PERCENT Hydrogen Fluoride (remainder HFC- PRESSURE (PSIA)365 mfc T = 20.2° C. T = 40.2° C. 0.0 15.53 29.42 6.8 18.15 32.19 100.06.65 13.98

The data also show that the vapor pressure of mixtures of1,1,1,3,3-pentafluorobutane and hydrogen fluoride is higher, at allindicated blend proportions, than 1,1,1,3,3-pentafluorobutane andhydrogen fluoride alone, i.e. as indicated in the first and last rowswhen hydrogen fluoride is 0.0 wt. % and 1,1,1,3,3-pentafluorobutane isat 100.0 wt. % as well as when 1,1,1,3,3-pentafluorobutane is at 0.0 wt.% and hydrogen fluoride is at 100.0 wt. %. The shift in composition withtemperature or pressure shows that 1,1,1,3,3-pentafluorobutane can beseparated from hydrogen fluoride by pressure swing distillation.

1. A process for removing 1,1,1,3,3-pentafluorobutane from a mixturecontaining 1,1,1,3,3-pentafluorobutane and at least one impurity, theprocess comprising adding hydrogen fluoride to a mixture containing1,1,1,3,3-pentafluorobutane and at least one impurity in an amountsufficient to form an azeotrope-like composition consisting essentiallyfrom about 90 weight percent to about 96 weight percent1,1,1,3,3-pentafluorobutane and from about 4 to about 10 weight percenthydrogen fluoride, and thereafter separating the azeotrope-likecomposition from the impurity.
 2. The process of claim 1 wherein theimpurity does not form an azeotropic mixture with1,1,1,3,3-pentafluorobutane, hydrogen fluoride or a mixture of 1,1,1,3,3pentafluorobutane and hydrogen fluoride.
 3. The process of claim 2wherein the impurity comprises a halocarbon.
 4. The process of claim 3wherein the impurity comprises 1,1,1,3,3-hexachlorobutane.
 5. Theprocess of claim 1 wherein the impurity is miscible with1,1,1,3,3-pentafluorobutane.
 6. The process of claim 1 wherein theseparating is conducted by distillation.
 7. The process of claim 1further comprising the step of separating 1,1,1,3,3-pentafluorobutanefrom an azeotropic mixture of 1,1,1,3,3-pentafluorobutane and hydrogenfluoride using pressure swing distillation.
 8. A method of forming anazeotrope-like composition which comprises blending from about 90 weightpercent to about 96 weight percent 1,1,1,3,3-pentafluorobutane and fromabout 4 to about 10 weight percent hydrogen fluoride, which compositionhas a vapor pressure of about 15 psia to about 22 psia at about 20.2° C.or a vapor pressure of above 29 psia to about 36 psia at about 40.2° C.